1. Field of the Invention
The present invention relates to a distance-measuring apparatus of a so-called active type, which measures a distance to an object by emitting a light beam toward the object and receiving a reflection beam from the object.
2. Related Background Art
An example of conventionally known distance-measuring apparatus of this type is what is disclosed in Japanese Laid-open Patent Application No. 2-222806. The apparatus has a light emitting element for selectively emitting a light beam toward a plurality of regions in a field and a light receiving element for receiving a reflected beam from an object irradiated by the emitted beam. The apparatus detects a region in which an output (receiving signal) from the light receiving element greatly changes and measures an object distance, based on a direction of the emitted beam to the detected region. Thus, the apparatus can measure a distance to a closest object among those in the plurality of regions thus irradiated, whereby for example in case two persons stand side by side in the field to be shot, the so-called mid-focused shooting, in which the apparatus is in focus with a portion between the two persons (i.e., with the background), can be prevented.
Also, Japanese Laid-open Patent Application No. 2-293615 discloses another distance-measuring apparatus, in which a light emitting element emits a beam divided into sections in the horizontal direction for example and is moved in the vertical direction, whereby the distance can be measured in a plurality of regions in the field in the vertical and horizontal directions. The apparatus selects a closest object distance from the measurement results to prevent the mid-focused shooting thereby as well.
Meanwhile, if in such distance-measuring apparatus of the active type a beam emitted from the light emitting element impinges on a border between a main object and the background, only a part of the emitted beam is reflected by the main object and then received by the light receiving element. In this case, the barycenter of the received beam is offset on the light receiving element from that of a beam supposed to be totally reflected, which could cause out-of-focus or unsharpness because of the inaccurate measurement result. Nevertheless, the apparatus as disclosed in the above applications prepared no means for such an error in distance measurement caused by the lack of received beam.